Daisy chained Joint Test Action Group (JTAG) registers result in long read/write times, as shifting even a small amount of common test data to multiple registers requires the entire chain to be shifted. Daisy chained JTAG registers result in long test data write cycles even if a small amount of test data needs to be replicated in multiple JTAG registers.
Two simple broadcast network designs have been discussed in the IEEE1687 standard documentation. One of the designs (Fig. E.16 Pg. 232 of the IEEE 1687 Standard document) offers the following scan chain configuration options: a) all the scan segments (JTAG register instances) configured in broadcast mode, or b) all the scan segments configured in daisy mode. Another design (Fig. E.15 Pg. 231 of the IEEE 1687 standard document) offers only the following scan chain configuration options: a) all of the scan segments (JTAG register instances) configured in broadcast mode, or b) exclusive read-out from only one scan segment at any given time.